bug: list -l shows raw numeric Unix mode for ZIP, inconsistent with TAR

[bug-ops]

Summary

exarch list -l shows permission modes in different formats for TAR vs ZIP archives:

# TAR output (clean POSIX)
-644          13 B  src/main.rs
d755           0 B  project/

# ZIP output (raw numeric)
-100644       13 B  src/main.rs
d40755         0 B  tests/

ZIP shows the raw external_attributes value from the central directory (including file type bits like S_IFREG = 100000, S_IFDIR = 040000) rather than the normalized POSIX permission string.

Expected behavior

Both formats should show the same normalized mode string, e.g. -rw-r--r-- or 644. The file type bits should be stripped from the display.